1. Field of the Invention
This invention relates to an apparatus for and a method of measuring the properties of individual particles in particle-suspended liquid and fractionating the particles on the basis of the result of the measurement.
2. Related Background Art
As an example of the apparatus of this kind, an apparatus as shown in FIG. 6 of the accompanying drawings has been put into practical use under the name of cell sorter. The basic principles of the cell sorter are also disclosed in U.S. Pat. Nos. 3,380,584, 3,710,933, 3,741,726, 3,826,364, etc.
In FIG. 6, sample liquid such as blood which is cell-suspended liquid and sheath liquid such as physiological salin solution are stored in a sample container 1 and a sheath container 2, respectively, and are pressurized by a compressor or a nitrogen gas cylinder and a regulator or the like and directed to a nozzle 5, from which the sample liquid and sheath liquid are injected as a fine stream 6 into the atmosphere. Consequently, by virtue of the sheath flow principle, the sample liquid is wrapped up in the sheath liquid and forms a fine stream in the sheath liquid and thus, the cells in the sample liquid flow one by one. By the vibration of a vibrator 7 mounted on the nozzle 5, the fine stream 6 later falls as droplets 8. A laser beam from a laser source 9 is applied to the intermediate portion of the fine stream 6, whereby the intensity of scattered light and the intensity of fluorescence emitted from the cells in the fine stream are metered by photodetectors 14 and 17, respectively. From the resulting measurement, the properties of the cells are analyzed on real time and in conformity with the result thereof, a charging voltage of positive or negative or 0 is applied to the fluid by charging means, not shown, whereby the droplets 8 are charged to positive or negative or 0. High voltage electrostatic deflecting plates 26a and 26b and disposed in opposed relationship with each other along the falling orbit of the droplets, and the falling cell droplets are deflected in directions conforming to the charges thereof and fall into different containers 27, 28 and 29. Thus, the cells can be fractionated and gathered in conformity with the properties thereof.
However, in the above-described particle fractionating apparatus according to the prior art, the cells must be charged immediately before they become droplets, and subtle regulation is required. Thus, it has been difficult to maintain a stable operation at all times.
Also, a high voltage must be handled, and this leads to a problem of involving a danger.
Further, basically, the cells can only be fractionated into three kinds of cells, i.e., cells charged to positive, cells charged to negative, and cells charged to neither. It would also appear reasonable to change the charging voltage into two strong and weak kinds and utilize the magnitude of the amount of deflection by the strength of the charging to divide the cells into five kinds, but this would lead to the problem that even if the charging can be accomplished accurately, the size, i.e. mass, of droplets will not always be constant and therefore the amount of deflection will vary and accurate fractionation cannot always be accomplished.